Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
6-19
Section 6 Theory of Operation
Issue 1.1
6.5.2 Remote Interface PWB
See Figures SD-11 through SD-13. The
remote interface PWB (A2A2) performs the
following functions:
x
Buffers all external transmitter remote
control inputs and provides the
connection for the system’s external
interlock circuit
x
Provides RF filtering for RF power probe
samples (forward power, reflected
power, and RF current)
x
Provides an isolated ATU serial interface
x
Converts external serial levels from TTL
to RS232 and RS422
x
RF monitor conditioning
x
Press-to-talk
input
x
Audio
conditioning
x
Audio
monitoring
x
Provides distribution and interface point
between the ac/dc distribution stages and
exciter control/monitor stage
6.5.2.1 Remote Inputs/Outputs
U7:A and associated components form the
circuitry to allow control of RF on/off when in
remote mode. U21:C and associated
components form the circuitry to control the
external interlock. If the link between TB1-19
and TB2-20 is open, U21:C will output a high
(external interlock), causing the transmitter to
inhibit RF power.
6.5.2.2 Isolated ATU Serial Interface
U9, U11, U13, U14, U15, and U17 provide
isolation to the internal serial bus (RS485) to
allow for ATU control. The ATU provides 5 V
to opto-isolators U13 and U14, which provide
isolation between differential transceivers
U11 and U17. The ATU controls the DE/RE
signal (J3-5), allowing the ATU to specify
direction of transmission through the isolated
link preventing collisions over the serial bus.
6.5.2.3 RS232 and RS422 Interface
U19, U18, U12, convert the TTL levels
produced by the control/display PWB to
RS232 and RS422 levels for external
control/monitoring of the transmitter.
6.5.2.4 RF Monitor Conditioning
U16 and associated components allow the
user to specify the RF monitor level from the
GUI. U23 and R163 form an adjustable gain
amplifier for the RF monitor signal that is able
to drive a 50
:
load.
6.5.2.5 Press-To-Talk Input
Link E4 allows for the selection of phantom
feed or normal press-to-talk operation. When
in position A, normal operation is selected
and grounding TB1-12 indicates press-to-talk
mode. When in position B, phantom feed
mode is selected and applying -15 V to the
shield (TB1-15) will indicate press-to-talk
mode.
6.5.2.6 Audio Conditioning
The audio conditioning circuitry on the remote
interface board consists of 3 parts, balanced
conditioning, audio filtering, and the audio
limiting.
6.5.2.6.1 Balanced Conditioning
U3:A and its associated components convert
the balance audio signal between TB1-14
and TB1-16 to an unbalanced signal. The
level of the audio signal is adjusted using
AUDIO LEVEL
potentiometer R37.
6.5.2.6.2 Audio Filtering
U8:B, U8:C, U8:D and their associated
components forms the audio input filter. This
filter, along with the poles located on the
Exciter Interface PWB and the Modulator
Filter, is a band pass filter passing signals
from 300 to 3000 Hz.
